Improved understanding of extent and size of tsunamigenic earthquakes through geodetic and tsunami datasets

This dissertation seeks to constrain the rupture size and magnitude of tsunamigenic earthquakes through the inclusion of data from both traditional geodetic instruments and recently deployed open-ocean tsunami gauges. First, I assess the sensitivity of the subduction zone model space to geodetic and tsunami waveform data. This provides a picture of where we can and cannot resolve rupture models when data is limited. It also highlights the issues that can ensue if poorly constrained models are used to study earthquakes. Second, I conduct an event-based joint inversion incorporating both geodetic and tsunami data for the 2015 Illapel, Chile earthquake. This includes merging codes for tsunami propagation, fault deformation, and linear inversions. The result of the joint inversion is a model space that is not only resolved near the coastline where geodetic data exists, but also near the trench where tsunami data is significantly more sensitive. The third component of this dissertation is an analysis of the feasibility of open-ocean data for rapid source inversions. This builds on current tsunami warning center methodologies but with a focus on the time constricted scenarios of a near-field warning from a local tsunami source. Here I analyze four different regions for their tsunamigenic potential as well as their potential to have instrumentation that will provide enough lead time during a local event to record data that is meaningful for disaster management and hazard warnings. The combination of these different aspects of tsunami-geodetic joint inversions illustrates both the improved model resolution and understanding of what was once a poorly constrained problem.Ph.D

Feasibility studies of terrestrial laser scanning in Coastal Geomorphology, Agronomy, and Geoarchaeology

Terrestrial laser scanning (TLS) is a newer, active method of remote sensing for the automatic detection of 3D coordinate points. This method has been developed particularly during the last 20 years, in addition to airborne and mobile laser scanning methods. All these methods use laser light and additional angle measurements for the detection of distances and directions. Thus, several thousands to hundreds of thousands of polar coordinates per second can be measured directly by an automatic deflection of laser beams. For TLS measurements, the coordinates and orientation of the origin of the laser beam can be determined to register different scan positions in a common coordinate system. These measurements are usually conducted by Global Navigation Satellite Systems or total station surveying, but also identical points can be used and data driven methods are possible. Typically, accuracies and point densities of a few centimetres to a few millimetres are achieved depending on the method. The derived 3D point clouds contain millions of points, which can be evaluated in post-processing stages by symbolic or data-driven methods. Besides the creation of digital surface and terrain models, laser scanning is used in many areas for the determination of 3D objects, distances, dimensions, and volumes. In addition, changes can be determined by multi-temporal surveys. The terrestrial laser scanner Riegl LMS Z-420i was used in this work in combination with the Differential Global Positioning System system Topcon Hiper Pro, based on Real Time Kinematic (RTK-DGPS). In addition to the direct position determination of the laser scanner, the position of a self-developed reflector on a ranging pole was measured by the RTK-DGPS system to accurately derive the orientation of each measured point cloud. Moreover, the scanner is equipped with an additional, mounted camera Nikon D200 to capture oriented pictures. These pictures allow colouring the point cloud in true colours and thus allow a better orientation. Furthermore, the pictures can be used for the extraction of detailed 3D information and for texturing the 3D objects. In one of the post-processing steps, the direct georeferencing by RTK-DGPS data was refined using the Multi Station Adjustment, which employs the Iterative Closest Point algorithm. According to the specific objectives, the point clouds were then filtered, clipped, and processed to establish 3D objects for further usage. In this dissertation, the feasibility of the method has been analysed by investigating the applicability of the system, the accuracy, and the post-processing methods by means of case studies from the research areas of coastal geomorphology, agronomy, and geoarchaeology. In general, the measurement system has been proven to be robust and suitable for field surveys in all cases. The surveys themselves, including the selected georeferencing approach, were conducted quickly and reliably. With the refinement of the Multi Station Adjustment a relative accuracy of about 1 cm has been achieved. The absolute accuracy is about 1.5 m, limited by the RTK-DGPS system, which can be enhanced through advanced techniques. Specific post-processing steps have been conducted to solve the specific goals of each research area. The method was applied for coastal geomorphological research in western Greece. This part of the study deals with 3D reconstructed volumes and corresponding masses of boulders, which have been dislocated by high energy events. The boulder masses and other parameters, such as the height and distance to the current sea level, have been used in wave transport equations for the calculation of minimum wave heights and velocities of storm and tsunami scenarios and were compared to each other. A significant increase in accuracy of 30% on average compared with the conventional method of simply measuring the axes was detected. For comparison, annual measurements at seven locations in western Greece were performed over three years (2009-2011) and changes in the sediment budget were successfully detected. The base points of the RTK-DGPS system were marked and used every year. Difficulties arose in areas with high surface roughness and slight changes in the annual position of the laser scanner led to an uneven point density and generated non-existing changes. For this reason, all results were additionally checked by pictures of the mounted camera and a direct point cloud comparison. Similarly, agricultural plants were surveyed by a multi-temporal approach on a field over two years using the stated method. Plant heights and their variability within a field were successfully determined using Crop Surface Models, which represent the top canopy. The spatial variability of plant development was compared with topographic parameters as well as soil properties and significant correlations were found. Furthermore, the method was carried out with four different types of sugar-beet at a higher resolution, which was achieved by increasing the height of the measurement position. The differences between the crop varieties and their growth behaviour under drought stress were represented by the derived plant heights and a relation to biomass and the Leaf Area Index was successfully established. With regard to geoarchaeological investigations in Jordan, Spain, and Egypt, the method was used in order to document respective sites and specific issues, such as proportions and volumes derived from the generated 3D models were solved. However, a full coverage of complexly structured sites, like caves or early settlements is partially prevented by the oversized scanner, slow measurement rates, and the necessary minimum measurement distance. The 3D data can be combined with other data for further research by the common georeference. The selected method has been found suitable to create accurate 3D point clouds and corresponding 3D models that can be used in accordance with the respective research problem. The feasibility of the TLS method for various issues of the case studies was proven, but limitations of the used system have also been detected and are described in the respective chapters. Further methods or other, newer TLS systems may be better suited for specific cases

Urban morphology analysis by remote sensing and gis technique, case study: Georgetown, Penang

This paper was analysed the potential of applications of satellite remote sensing to urban planning research in urban morphology. Urban morphology is the study of the form of human settlements and the process of their formation and transformation. It is an approach in designing urban form that considers both physical and spatial components of the urban structure. The study conducted in Georgetown, Penang purposely main to identify the evolution of urban morphology and the land use expansion. In addition, Penang is well known for its heritage character, especially in the city of Georgetown with more than 200 years of urban history. Four series of temporal satellite SPOT 5 J on year 2004, 2007, 2009 and 2014 have been used in detecting an expansion of land use development aided by ERDAS IMAGINE 2014. Three types of land uses have been classified namely build-up areas, un-built and water bodies show a good accuracy with achieved above 85%. The result shows the built-up area significantly increased due to the rapid development in urban areas. Simultaneously, this study provides an understanding and strengthening a relation between urban planning and remote sensing applications in creating sustainable and resilience of the city and future societies as well

Resolving the Kinematics and Moment Release of Early Afterslip within the First Hours following the 2016 M_w 7.1 Kumamoto Earthquake: Implications for the Shallow Slip Deficit and Frictional Behavior of Aseismic Creep

As stresses following rupture are dissipated continuous measurements of postseismic surface deformation provide insight into variations of the frictional strength of faults and the rheology of the lower crust and upper mantle. Due to the difficulty of capturing the earliest phase of afterslip, most analyses have focused on understanding postseismic processes over timescales of weeks to years. Here we investigate the kinematics, moment release, and frictional properties of the earliest phase of afterslip within the first hours following the 2016 M_w 7.1 Kumamoto earthquake using a network of 5‐minute sampled continuous Global Positioning System (GPS) stations. Using independent component analysis to filter the GPS data, we find that (1) early afterslip contributes only ~1% of total moment release within the first hour and 8% after 24 hr. This suggests that the lack of a coseismic slip deficit, which we estimate using standard geodetic data sets (e.g., InSAR, GPS, and pixel offsets) and which span the first 4 days of the postseismic period, is largely reflective of the dynamic rupture process and we can rule out contamination of moment release by early afterslip. (2) Early afterslip shows no evidence of a delayed nucleation or acceleration phase, where instead fault patches transition to immediate deceleration following rupture that is consistent with frictional relaxation under steady state conditions with dependence only on the sliding velocity. (3) There is a close correlation between the near‐field aftershocks and afterslip within the first hours following rupture, suggesting afterslip may still be an important possible triggering mechanism during the earliest postseismic period

Discriminating the occurrence of inundation in tsunami early warning with one-dimensional convolutional neural networks

Tsunamis are natural phenomena that, although occasional, can have large impacts on coastal environments and settlements, especially in terms of loss of life. An accurate, detailed and timely assessment of the hazard is essential as input for mitigation strategies both in the long term and during emergencies. This goal is compounded by the high computational cost of simulating an adequate number of scenarios to make robust assessments. To reduce this handicap, alternative methods could be used. Here, an enhanced method for estimating tsunami time series using a one-dimensional convolutional neural network model (1D CNN) is considered. While the use of deep learning for this problem is not new, most of existing research has focused on assessing the capability of a network to reproduce inundation metrics extrema. However, for the context of Tsunami Early Warning, it is equally relevant to assess whether the networks can accurately predict whether inundation would occur or not, and its time series if it does. Hence, a set of 6776 scenarios with magnitudes in the range Mw 8.0–9.2 were used to design several 1D CNN models at two bays that have different hydrodynamic behavior, that would use as input inexpensive low-resolution numerical modeling of tsunami propagation to predict inundation time series at pinpoint locations. In addition, different configuration parameters were also analyzed to outline a methodology for model testing and design, that could be applied elsewhere. The results show that the network models are capable of reproducing inundation time series well, either for small or large flow depths, but also when no inundation was forecast, with minimal instances of false alarms or missed alarms. To further assess the performance, the model was tested with two past tsunamis and compared with actual inundation metrics. The results obtained are promising, and the proposed model could become a reliable alternative for the calculation of tsunami intensity measures in a faster than real time manner. This could complement existing early warning system, by means of an approximate and fast procedure that could allow simulating a larger number of scenarios within the always restricting time frame of tsunami emergencies.Tide gauge data were obtained from the Sea Level Station Monitoring Facility of the Intergovernmental Oceanographic Commission (http://www.ioc-sealevelmonitoring.org/list.php). The coarser bathymetric and topographic data from the General Bathymetric Chart of the Ocean (https://www.gebco.net/data_and_products/gridded_bathymetry_data/). The authors acknowledge SHOA for providing nautical charts and coastal zone plans used to generate high resolution topo-bathymetric grids for research purposes. We are deeply grateful with A. Gubler that prepared a first version of the high resolution bathymetry grids. The authors acknowledge the computer resources at CTE-POWER (https://www.bsc.es/supportkc/docs/CTE-POWER/overview) and the technical support provided by BSC. We are greatly thankful the EDANYA Group at Málaga University for sharing the Tsunami-HySEA code. Most figures were generated with Python91,92,93 and Global Mapping Tools94. JN deeply thanks support of Mitiga Solutions during his secondment. PAC would like to thank funding by ANID, Chile Grants FONDEF ID19I10048, Centro de Investigación para la Gestión Integrada del Riesgo de Desastres (CIGIDEN) ANID/FONDAP/15110017, and Centro Científico Tecnológico de Valparaíso, ANID PIA/APOYO AFB180002. NZ has received funding from the Marie Skłodowska-Curie grant agreement H2020-MSCA-COFUND-2016-75443.Peer ReviewedPostprint (published version

Coupled, Physics-Based Modeling Reveals Earthquake Displacements are Critical to the 2018 Palu, Sulawesi Tsunami

The September 2018, Mw 7.5 Sulawesi earthquake occurring on the Palu-Koro strike-slip fault system was followed by an unexpected localized tsunami. We show that direct earthquake-induced uplift and subsidence could have sourced the observed tsunami within Palu Bay. To this end, we use a physics-based, coupled earthquake–tsunami modeling framework tightly constrained by observations. The model combines rupture dynamics, seismic wave propagation, tsunami propagation and inundation. The earthquake scenario, featuring sustained supershear rupture propagation, matches key observed earthquake characteristics, including the moment magnitude, rupture duration, fault plane solution, teleseismic waveforms and inferred horizontal ground displacements. The remote stress regime reflecting regional transtension applied in the model produces a combination of up to 6 m left-lateral slip and up to 2 m normal slip on the straight fault segment dipping 65∘ East beneath Palu Bay. The time-dependent, 3D seafloor displacements are translated into bathymetry perturbations with a mean vertical offset of 1.5 m across the submarine fault segment. This sources a tsunami with wave amplitudes and periods that match those measured at the Pantoloan wave gauge and inundation that reproduces observations from field surveys. We conclude that a source related to earthquake displacements is probable and that landsliding may not have been the primary source of the tsunami. These results have important implications for submarine strike-slip fault systems worldwide. Physics-based modeling offers rapid response specifically in tectonic settings that are currently underrepresented in operational tsunami hazard assessment

Tsunamis from source to coast

Tsunami disasters pose a significant threat to coastal communities. In the last decades, tsunamis caused enormous destruction and exceeding 250000 fatalities. International efforts led to sig-nificant advances in tsunami science and research, but recent events demonstrated some limi-tations. Thus, it is essential to increase our knowledge of the source to coast tsunami phenom-enon. A better understanding of potential tectonic structures and other generation mechanisms is needed, especially in complex geologic domains or where sources are unknown. Furthermore, we need to improve Tsunami Warning Systems (TWSs) to provide timely alerts for communi-ties in the near field. Therefore, potential tsunamigenic sources in the diffuse plate boundary setting and the near field of the southwest Iberian margin (SWIM) are investigated. For the March 31, 1761, trans-atlantic tsunami, numerical modelling has been used to propose a structure that agrees with tsunami travel times, tsunami observations, macroseismic data, and kinematic plate modelling. Since there exists a description of a tsunami for the November 11, 1858, Sétubal earthquake, its source has been investigated using macroseismic analysis. The analysis suggests a local structure in a compressive regime with weak to moderate tsunamigenic potential. Future tsu-nami hazard assessments need to include the sources of the investigated events. To quickly estimate the tsunami impact, the Tsunami Runup Predictor (TRP), an empirical source-to-coast method to instantly provide first-order estimates of the tsunami runup based on waveform parameters has been developed. The TRP is helpful for emergency managers and evacuation planning for near-field events. Moreover, the author of this thesis contributed to the tsunami impact assessment of September 28, 2018, Palu tsunami, where tsunamis generated by multiple sources caused runup heights up to 9.2 m. However, for local sources, tsunami warning remains challenging; thus, communities need to be prepared how to respond appropriately to earthquakes and tsunamis with or without warning

Volcanic Processes Monitoring and Hazard Assessment Using Integration of Remote Sensing and Ground-Based Techniques

The monitoring of active volcanoes is a complex task based on multidisciplinary and integrated analyses that use ground, drones and satellite monitoring devices. Over time, and with the development of new technologies and increasing frequency of acquisition, the use of remote sensing to accomplish this important task has grown enormously. This is especially so with the use of drones and satellites for classifying eruptive events and detecting the opening of new vents, the spreading of lava flows on the surface or ash plumes in the atmosphere, the fallout of tephra on the ground, the intrusion of new magma within the volcano edifice, and the deformation preceding impending eruptions, and many other factors. The main challenge in using remote sensing techniques is to develop automated and reliable systems that may assist the decision maker in volcano monitoring, hazard assessment and risk reduction. The integration with ground-based techniques represents a valuable additional aspect that makes the proposed methods more robust and reinforces the results obtained. This collection of papers is focused on several active volcanoes, such as Stromboli, Etna, and Volcano in Italy; the Long Valley caldera and Kilauea volcano in the USA; and Cotopaxi in Ecuador

Slip Distribution Of Large Earthquakes In Greece

Η εκτίμηση της χωρικής και χρονικής κατανομής της ολίσθησης στην επιφάνεια του ρήγματος αποτελεί σημαντικό εργαλείο για τους σεισμολόγους και όλους τους γεω-επιστήμονες για την κατανόηση της χωροχρονικής εξέλιξης της σεισμικής διάρρηξης. Μια τέτοια διαδικασία απαιτεί δεδομένα τα οποία προσδιορίζονται μετά από ένα ισχυρό σεισμικό γεγονός, δηλαδή τις εστιακές παραμέτρους, συμπεριλαμβανομένου του μηχανισμού γένεσης και τη γεωμετρία του ρήγματος. Η μέθοδος αντιστροφής του τανυστή ολίσθησης μπορεί να συμβάλλει στη δημιουργία αξιόπιστων χαρτών κατανομής εδαφικής κίνησης (shakemaps), στη γρήγορη αντίδραση της πολιτείας μετά από μεγάλο σεισμό και στην εκτίμηση πιθανότητας εκδήλωσης μετασεισμών. Το λογισμικό LinSlipInv (Gallovic and Zahradnik, 2011; Gallovic et al., 2014) εκτελείται χρησιμοποιώντας τοπικά και περιφερειακά δεδομένα που έχουν καταγραφεί από σεισμογράφους του Ενιαίου Εθνικού Δικτύου Σεισμογράφων (ΕΕΔΣ), καθώς και από τα δίκτυα επιταχυνσιογράφων του Γεωδυναμικού Ινστιτούτου του Εθνικού Αστεροσκοπείου Αθηνών (ΓΙ-ΕΑΑ), του Ινστιτούτου Τεχνικής Σεισμολογίας και Αντισεισμικών Κατασκευών (ΙΤΣΑΚ) και, για το Ανατολικό Αιγαίο, δεδομένα από Kandilli Observatory and Earthquake Research Institute (KOERI) και το Κεντρικό Σύστημα Δεδομένων Σεισμών της Τουρκίας (AFAD). Εξετάστηκαν επιλεγμένοι ισχυροί σεισμοί (με Mw ≥ 6.0) που έγιναν κατά την τελευταία πενταετία σε διάφορες περιοχές της ελληνικής επικράτειας. Κατά τον προσδιορισμό της κατανομής ολίσθησης μέσω του λογισμικού LinSlipInv, εξετάστηκαν οι μηχανισμοί γένεσης, τα μοντέλα ταχύτητας και η γεωμετρία των ρηγμάτων από ήδη δημοσιευμένες εργασίες. Τα αποτελέσματα της κατανομής ολίσθησης χρησιμοποιήθηκαν ως δεδομένα εισόδου για τον υπολογισμό της εδαφικής παραμόρφωσης, χρησιμοποιώντας το πρόγραμμα DIS3D (Erickson, 1987), λαμβάνοντας υπόψη ότι δεν παρατηρήθηκε ίχνος του ρήγματος στην επιφάνεια. Η προκύπτουσα κατανομή ολίσθησης και η εδαφική παραμόρφωση συγκρίθηκαν με εκείνες που προσδιορίστηκαν από άλλες μελέτες, συμπεριλαμβανομένων εκείνων που χρησιμοποιούν τεχνικές συμβολομετρίας InSAR και GNSS. Τα αποτελέσματα της κατανομής ολίσθησης κρίνονται ικανοποιητικά. Η κατανομή ολίσθησης για τον σεισμό της Κεφαλονιάς που έλαβε χώρα στις 26 Ιανουαρίου 2014, και προέκυψε από την εφαρμογή του λογισμικού LinSlipInv χρησιμοποιώντας δεδομένα σε τοπικές έως και περιφερειακές αποστάσεις, ανέδειξε ένα επεισόδιο διάρρηξης, ήτοι μία σεισμική πηγή, με μέγιστη ολίσθηση ίση με 40 cm. Όσον αφορά στην εδαφική παραμόρφωση που προέκυψε από την υπολογισθείσα κατανομή ολίσθησης, οι τιμές στην οριζόντια και κατακόρυφη συνιστώσα είναι χαμηλές, κυρίως λόγω του μεγέθους και του εστιακού βάθους του σεισμού. Τα αποτελέσματα έδειξαν μέγιστη τιμή οριζόντιας μετατόπισης 2 cm, ανατολικά του ρήγματος, γύρω από το Αργοστόλι. Η ολίσθηση για τον σεισμό της Λήμνου στις 24 Μαΐου 2014 ανέδειξε μια πολύπλοκη πηγή, η οποία αποτελείται από τρία διακριτά υπο-γεγονότα. Τα στιγμιότυπα της ολίσθησης αποκάλυψαν ότι αυτή κατευθύνθηκε προς την οροφή του ρήγματος, ενώ η μέγιστη τιμή έφτασε τα 1.4 m, εμφανίζοντας μια δικαντευθυντική διάρρηξη. Πιο συγκεκριμένα, παρατηρήθηκε μια αρχική διάδοση προς τα δυτικά, ακολουθούμενη από ένα μεγάλο επεισόδιο ολίσθησης προς τα ανατολικά. Η παραγόμενη εδαφική παραμόρφωση στη Λήμνο δείχνει δεξιόστροφη οριζόντια κίνηση. Τα τοπικά έως περιφερειακά δεδομένα που χρησιμοποιήθηκαν στην αντιστροφή της ολίσθησης για τον σεισμό της Λευκάδας της 17ης Νοεμβρίου 2015 αποκάλυψαν κατευθυντικότητα προς τα ΝΝΔ. Επιπλέον, αναγνωρίστηκαν δύο σεισμικές πηγές, ενώ η μέγιστη τιμή ήταν 1.2 m. Όσον αφορά στην εδαφική παραμόρφωση, η δεξιόστροφη κίνηση επιβεβαιώθηκε με τα αποτελέσματα που προέκυψαν στην παρούσα μελέτη, χρησιμοποιώντας το λογισμικό DIS3D. Παρατηρήθηκαν μικρές τιμές ανύψωσης για το νότιο τμήμα της Λευκάδας (μέγιστη ανύψωση 7 cm). Σύμφωνα με τα αποτελέσματα αναστροφής του LinSlipInv για τον σεισμό της Λέσβου που συνέβη στις 12 Ιουνίου 2017, η μέγιστη ολίσθηση ήταν ~ 1.0 m και εντοπίστηκε μία μοναδική πηγή. Η εξέλιξη της διάρρηξης, όπως αποκαλύφθηκε από τα στιγμιότυπα ολίσθησης ανά 1 δευτερόλεπτο, έδειξε ένα μοναδικό επεισόδιο ολίσθησης και διάρρηξη προς τα ΒΔ, η οποία θα μπορούσε να εξηγήσει εν μέρει τις βλάβες που παρατηρήθηκαν στο χωριό Βρίσα. Η εφαρμογή του λογισμικού DIS3D ανέδειξε οριζόντια κίνηση προς τα ΒΒΑ στη Νήσο Λέσβο. Επιπλέον, εντοπίστηκε καθίζηση που φθάνει τα 20 cm στα νότια παράλια, πλησίον του σεισμογόνου ρήγματος. Τα αποτελέσματα κατανομής ολίσθησης που προέκυψαν για τον σεισμό της 20ης Ιουλίου 2017 στην Κω παρουσίασαν μία μοναδική πηγή με μέγιστη τιμή ολίσθησης 1.8 m. Το προτεινόμενο ρήγμα είναι αυτό που κλίνει προς βορρά. Όσον αφορά την εδαφική παραμόρφωση, εντοπίστηκε μετατόπιση με διεύθυνση περίπου Β-Ν. Τιμές οριζόντιας μετάθεσης, της τάξης των 5 cm, εντοπίστηκαν στη Χερσόνησο της Μαρμαρίδας. Στον κόλπο Γκόκοβα εντοπίστηκε καθίζηση που έφθανε τα 30 cm.The temporal and spatial slip distribution assessment is a vital tool for seismologists and other geoscientists towards understanding the spatiotemporal evolution of the earthquake rupture. Such an evaluation requires data which are typically extracted after a large event, meaning the earthquake’s source parameters, including focal mechanism, fault geometry and hypocentral relocation. The slip inversion method has application potential for shakemaps, emergency response and aftershock hazard assessment. The LinSlipInv software (Gallovic and Zahradnik, 2011; Gallovic et al., 2014) is implemented using local and near-regional data recorded by seismographs belonging to the Hellenic Unified Seismological Network (HUSN), as well as by the accelerometric network of the Geodynamic Institute of the National Observatory of Athens (GI-NOA), the Institute of Engineering Seismology & Earthquake Engineering (ITSAK) and for the eastern regions, the Kandilli Observatory and Earthquake Research Institute (KOERI) and the Turkey Earthquake Data Center System (AFAD). Selected strong earthquakes (with Mw ≥ 6.0) that occurred during the last decade in various regions of the Hellenic territory are examined. Towards the slip distribution determination via LinSlipInv, focal mechanisms, velocity models and fault geometries, were examined. The slip distribution results were used as input to extrapolate ground deformation using the DIS3D Program (Erickson, 1987), even in cases where no surficial trace of the fault is observed. The obtained slip distribution and crustal deformation are compared with the ones determined by other studies, including InSAR and GPS. The slip distribution results were promising. The results for the 26 January 2014 Cephalonia event, derived by the LinSlipInv software utilizing local and near-regional data, indicate a single rupture episode, with the maximum slip calculated at 40 cm. Concerning the ground deformation derived by the obtained slip distribution, the values in the horizontal and vertical component are low, mainly due to the magnitude and the focal depth of the event. The results revealed a maximum of 2 cm of horizontal displacement, to the east of the fault, on Cephalonia Island. The calculated slip of the 24 May 2014 Lemnos earthquake revealed a complex source, comprised of three discrete patches. The slip snapshots revealed that the slip migrated updip, whereas the total maximum slip value reached 1.4 m. In addition, the slip velocity snapshots identified a bilateral rupture. More specifically, an initial westward rupture propagation was observed, followed by a major slip patch heading to the east. The obtained ground deformation results in Lemnos indicate a right lateral horizontal movement. The local to near-regional slip inversion results for the 17 November 2015 Lefkada event revealed directivity towards the SSW. In addition, two slip episodes can clearly be identified, whereas the maximum obtained slip value was 1.2 m. Regarding the ground deformation, the dextral movement was verified by the herein obtained results, using the DIS3D software. Small uplift values were obtained for the southern part of the Lefkada Island (7 cm maximum uplift). According to the LinSlipInv inversion results for the 12 June 2017 Lesvos earthquake, the maximum slip was ~1.0 m and a single patch was identified. The space-time rupture evolution, as revealed by slip velocity snapshots obtained per 1 s, indicated a unique slip patch and rupture directivity towards the NW, which could partly explain the damage observed in the Vrissa village. However, extended destruction is also due to other factors, such as soil conditions and vulnerability of the buildings. An extensional regime and a NNE horizontal movement on the Lesvos Island were identified by the application of the DIS3D software along with subsidence reaching 20 cm offshore, in the vicinity of the causative fault. The slip distribution results derived by the LinSlipInv software for the 20 July 2017 Kos earthquake presented a unique patch with a maximum slip value of 1.8 m. The suggested causative fault is the one dipping to the north. Regarding the ground deformation, a N-S extension is observed. Values of horizontal movement of the order of 5 cm were obtained in Marmaris. Subsidence up to 30 cm was identified in the Gökova gulf

Geodetic and Seismological Investigations of Earthquake Cycle Deformation and Fault Zone Properties

A number of geologic processes on the surface and in the interior of the Earth result in ground deformation on human timescales. These processes include the steady motion of tectonic plates, the internal deformation of heterogeneous regions in the crust, the response of the Earth to surface loads, and deformation at plate boundaries, all acting to produce millimeter-scale displacements each year. These same processes are also responsible for many natural hazards that cause harm to human communities: earthquakes and tsunamis are the most directly related, but sea level rise and extreme flooding are also pertinent natural threats exacerbated by the deformation of the ground. In order to understand these natural hazards and to mitigate their impacts, it is important to quantify surface deformation and to understand the physical mechanisms underlying it. The chapters of this dissertation address several questions in the field of tectonic deformation that relate to these processes. In particular, I focus on understanding earthquake hazards and fault zone properties using a variety of tools at the intersection of space geodesy and seismology. Zones of weakness in the Earth’s crust at all scales are relevant for the study of natural hazards. They respond to external stresses and often host earthquake ruptures. Fault zones, as one small-scale example, are thought to be mechanically weaker than their surroundings because the accumulated near-fault damage results in lower mechanical strength, forming compliant fault zones. Importantly, the presence of a compliant fault zone around a fault affects the types of earthquake ruptures the fault can sustain. In order to study compliant fault zones around a major fault, I investigated the elastic properties of the crust near the San Andreas Fault Zone in northern California. I used GPS measurements to characterize compliant fault structures along strike and found that their distribution is heterogeneous even over short spatial scales. Larger zones of weakness also impact present-day deformation. On continental scales, inherited zones of weakness from previous tectonic episodes can affect the seismic activity of a region even millions of years later. In the craton of southern Africa, I studied the rupture process of a rare M6.5 earthquake in Botswana that ruptured the lower crust in a continental plate interior. Using a joint analysis of teleseismic waveforms, InSAR data, and relocated aftershocks, I identified the rupture plane out of the two possible focal planes. The modeled strike matches with the boundary of an ancient collisional mountain belt that has been reactivated in the present day as a set of normal faults. Intraplate earthquakes such as this one are challenging to forecast because they occur in regions of low interseismic strain, but they can be especially damaging because they occur in places that aren’t expecting earthquakes. Understanding the structure of pre-existing weak zones in the crust may be key in such situations. Clues to the internal structure of the crust may also come from the study of periodic hydrological loads on the Earth’s surface. Seasonal loads from snow, rivers, lakes, groundwater, the ocean, and the atmosphere cause surface deformation that depends on the structure of the underlying medium and the processes involved. In order to analyze these processes in a tectonically active region, I performed a study on hydrological loading in GPS data from South Asia and Southeast Asia, a region impacted by a strong yearly monsoon. The annual deformation varies across the region but is generally consistent with the elastic loading modeled from an independent gravity dataset. The appropriate modeling of the hydrological loading deformation in the future could help quantify the storage of aquifers, improve our understanding of earthquake cycle deformation, and aid in the accurate detection of transient fault behavior. The remaining two chapters of this dissertation relate to transient fault behavior of the Mendocino Triple Junction in northern California. This region lies at the intersection of three major plate-bounding faults, and it produces some of the largest earthquakes in California. Several of the plate-bounding faults at the Mendocino Triple Junction produce a mix of seismic and aseismic moment release; this results in fascinating time-dependent slip behavior and an interplay between aseismic and seismic slip modes. In one study of this behavior, I used characteristically repeating earthquakes to identify regions of the Mendocino Fault Zone that are creeping aseismically. Using a dataset from 2008 to 2018, I found several dozen families of small-magnitude repeating earthquakes that show a high degree of active creep on the plate boundary fault. The creep rate is calculated to be about 65% of the overall slip budget, a significant amount but in line with previous estimates of aseismic slip on oceanic transform faults. During this time interval, the slip appears to be relatively steady, but the repeating earthquake catalog allows us to study any time-dependent variations of the creep rate in the future. On the neighboring Cascadia Subduction Zone, I also find aseismic creep with time-dependent rate variations. Well-known slip transients called Episodic Tremor and Slip events occur on the southern Cascadia Subduction Zone margin every 7-10 months, resulting in several centimeters of slip at about 30 km depth. However, in the final chapter of this dissertation, I document changes in surface velocity that appear uncorrelated with the process of Episodic Tremor and Slip. I find that surface GPS velocities near the Mendocino Triple Junction show systematic variations in their east/west component that last for several years apiece. The timing of several velocity changes is coincident with the timing of large (M>6.5) offshore earthquakes. The spatial pattern and temporal pattern of the observations do not indicate more usual processes like afterslip, viscoelastic relaxation, or hydrological loading are sufficient to explain the observations. Instead, inversion of the velocity changes suggests that in a region slightly updip of the Episodic Tremor and Slip portion of the interface, interseismic coupling may both increase and decrease in connection with the offshore earthquakes. A speculative dynamic triggering mechanism is presented. Such observations suggest that understanding fault zone properties is of paramount importance in the study of earthquake hazards. The findings also show that in light of newer geodetic and seismological datasets, there is still much to be learned and many unanswered questions about the behavior of fault zones throughout the earthquake cycle